Intratumoral heterogeneity and TERT promoter mutations in progressive/higher-grade meningiomas

Abstract

Background: Recent studies have reported mutations in the telomerase reverse transcriptase promoter (TERTp) in meningiomas. We sought to determine the frequency, clonality and clinical significance of telomere gene alterations in a cohort of patients with progressive/higher-grade meningiomas.

Methods: We characterized 64 temporally- and regionally-distinct specimens from 26 WHO grade III meningioma patients. On initial diagnoses, the meningiomas spanned all WHO grades (3 grade I, 13 grade II and 10 grade III). The tumor samples were screened for TERTp and ATRX/DAXX mutations, and TERT rearrangements. Additionally, TERTp was sequenced in a separate cohort of 19 patients with radiation-associated meningiomas. We examined the impact of mutational status on patients' progression and overall survival.

Results: Somatic TERTp mutations were detected in six patients (6/26 = 23%). Regional intratumoral heterogeneity in TERTp mutation status was noted. In 4 patients, TERTp mutations were detected in recurrent specimens but not in the available specimens of the first surgery. Additionally, a TERT gene fusion (LPCAT1-TERT) was found in one sample. In contrary, none of the investigated samples harbored an ATRX or DAXX mutation. In the cohort of radiation-induced meningiomas, TERTp mutation was detected in two patients (10.5%). Importantly, we found that patients with emergence of TERTp mutations had a substantially shorter OS than their TERTp wild-type counterparts (2.7 years, 95% CI 0.9 - 4.5 years versus 10.8 years, 95% CI 7.8 -12.8 years, p=0.003).

Conclusions: In progressive/higher-grade meningiomas,TERTp mutations are associated with poor survival, supporting a model in which selection of this alteration is a harbinger of aggressive tumor development. In addition, we observe spatial intratumoral heterogeneity of TERTp mutation status, consistent with this model of late emergence in tumor evolution. Thus, early detection of TERTp mutations may define patients with more aggressive meningiomas. Stratification for TERT alterations should be adopted in future clinical trials of progressive/higher-grade meningiomas.

Keywords: fusion; heterogeneity; meningioma; rearrangements; telomere.

Figure 1

Axial post-gadolinium T1-weighted images showing the TERTp wild-type sphenoid wing meningioma WHO grade II (Case Pat24) (A) pre- and (B) postoperatively. An adjuvant treatment was not pursued after initial resection. (C) 22 months later the patient showed a local recurrent tumor. At that time point, the tumor was histologically progressive to grade III and carried a newly detected TERTp mutation. The patient had a rapidly progressive subsequent course, and died 6 months after the second surgery.

Figure 2

An axial post-gadolinium T1-weighted image showing the TERTp wild-typeconvexity WHO grade II meningioma (case Pat08) (A). A radiation therapy with 60 Gy was applied after a subtotal tumor resection (B) and the patient was progression-free for 12 months. The follow-up MRI showed a progressive tumor (C) and the pathological diagnosis was consistent with an anaplastic meningioma WHO grade III with a new developed TERTp mutation. While the recurrence in (D) was proven to be TERTp wild-type, the subsequent recurrence (E) was TERTp-mutant. At the time of last surgery (F), the TERTp mutation was detected in the right-sided, but not in the left-sided meningioma. The patient passed away 22 months after the first emergence of TERTp mutation due to progressive disease.

Figure 3. Spatial representation of the tumor from Figure 2C for TERTp mutation status

The sequencing of TERTp mutation on DNA extracted from 8 different paraffin embedded tumor blocks from the surgical resection specimen to provide a widely spread and independent geographical separation for the sampling. Although we are not able to directly localize these block specimens with the MRI scan, sequencing revealed a mutation in 5 out of 8 samples, providing evidence for spatial intratumoral heterogeneity in TERTp mutant meningiomas.

Figure 4. Kaplan-Meier estimates of progression and overall survival in grade II and III meningioma in relation to TERTp mutation status

Patients with a TERTp mutation had a significantly shorter progression-free survival (1.1 years, 95% CI 0.8 - 1.4 versus 3.6 years, 95% CI 0.3 - 9.6, p= 0.002). Likewise, overall survival was significantly shorter in TERTp-mutant compared with wild-type patients (2.7 years, 95% CI 0.9 – 4.5 versus 10.8 years, 95% CI 7.8 -12.8, p=0.003).

Figure 5

(A) A fusion was detected between exon 11 of LPCAT1 (orange) and exon 2 of TERT (gray) within chromosome 5p15. 33. (B) TERT expression (reverse transcriptase PCR) in three subsequent samples of patient 13 with TERT rearrangements compared to three samples from patients without TERT alterations. TERT was amplified in all consecutive samples. GAPDH was used as a control. (C) Representative MRIs for tumor growth history for patient 13.